>The net energy output is only around 1.3 so an acre of corn produces maybe 400 gallons of gasoline equivalent output requires 300 gallons of gasoline equivalent in energy inputs.

What is the problem, that sounds great? 30% free output out of your input is staggering honestly. Thank you sunshine and atmospheric CO2. You don't have to use fossil fuel for this. You can potentially run the farm equipment off ethanol if it were designed as such.

You can also only grow sugarcane well up to usda zone 8. Some people can do it as an annual but I guess it is tricky. Corn you can grow all the way into Canada.

> What is the problem, that sounds great? 30% free output out of your input is staggering honestly.

It's really not when you compare it to the energy return you get from energy invested in other forms of energy generation. Solar power, for example, is typically estimated to produce 13x as much energy as it takes to make the panel. This is obviously a considerable improvement over 1.3x.

So why does it matter as long as the net energy output is positive? Because the whole point of the energy generating exercise is to do something with the output energy other than just make more energy and there isn't unlimited capacity on the input side of the equation. The 100 "free" gallons you get in the example sounds great, but sustaining that requires inputting (i.e. growing) 300 gallons worth, so you need to produce 400 gallons total to get 100 useful gallons. Looking at the math another way, an ethanol powered civilization would spend 75% of the energy it produces simply producing more energy, leaving only 25% to actually do anything useful with. This is bad, because said civilization will run out land to grow corn for ethanol well before it's generating enough useful energy.

It's sort of like the energy equivalent of the food explanation for why it took human civilization so long to advance out of the agrarian stage. Up until relatively recently, most humans spent most of their time and effort simply growing enough food to live. This left very little excess capacity for humans to do anything to move humanity forward. In the modern day, very little of our time and energy goes into growing food, leaving all sorts of extra capacity to build spaceships and AI and the Internet and whatever else. But only because we got really efficient at growing food.

Yeah, but market pricing fluctuates and that corn (hopefully) isn't grown in a monocrop. Alternating with soybean affects protein and food oils markets, and alternating or adding industrial hemp both, plus tremendous fibre.

Opportunity costs essentially. The effort that goes into growing and refining corn ethanol could be better spent on reducing fuel consumption instead of dedicating five acres of land to provide the equivalent net yearly fossil fuel consumption of a single average car using 500 gallons of gasoline to drive about 15000 miles.

Why not do both, reduce fuel consumption while shifting to a carbon neutral fuel source that is fully onshored?

Again opportunity costs. It almost always makes sense to spend the money on the most efficient means to achieve the goal. Money spent paying farmers and ethanol refiners to inefficiently produce 25% lower carbon fuel could instead be directed at other endeavours that for the same cost reduce carbon emissions more.

The difference is we already grow corn at scale beyond market need. Probably less has to be paid in that effort than starting up some other industry. Which still can be done along side the corn shouldering the load until that industry reaches the scale of the corn industry's waste product.

> Probably less has to be paid in that effort than starting up some other industry.

No, that's the entire point. As mentioned above, for ethanol you input the equivalent of 300 ethanol gallons worth of energy (which could also be ethanol) to get 100 net gallons out you can do whatever you want with. If you instead used that 300 gallons worth of input to produce solar panels, they'd produce 3,600 net gallons worth of equivalent energy over their lifetime. You get 36x more net energy building solar panels than growing corn for ethanol. Sure, you could spend 600 gallons worth of energy and do both, but then you'd still be better off switching the entire 600 gallons of input to solar panels until you run out of solar panel generation capacity or demand. That's the opportunity cost.

Also a minor point worth making is that ethanol is in no way a "waste product" from the corn growing industry that would otherwise go to, well, waste. Farmers aren't just growing a bunch of extra corn for no reason that we can conveniently use for ethanol. If demand for ethanol stopped, they'd stop growing all that extra corn.